Science fiction
Science fiction is a genre of story telling setting out alternatives to what is currently considered scientifically possible or creating extrapolations from present-day knowledge. It is generally set in the future and often in non-Terrestrial locales, but science fiction tales may be set in the past as well, particularly through the use of story lines involving alternate history and time travel. It is found in short stories, novels, motion pictures, television shows and radio. Science fiction is generally considered to have been introduced in the nineteenth century by authors such as Jules Verne, Edgar Allan Poe, and H.G. Wells, although elements of what would come to be called science fiction can be found in earlier literature as well. The genre became more widely popular in the second half of the twentieth century. Once a fringe genre, today science fiction is not only mainstream, but has spawned a number of sub-genres, including speculative fiction and the space opera. What constitutes true science fiction and what crosses over into other categories, including fantasy and horror, are subjects of heated discussion among aficionados.